Adjustable implant with self-sealing elastomeric membrane and methods of fabrication thereof

ABSTRACT

An adjustable implant for volumetrically altering, replacing, expanding, or augmenting tissues is provided. The implant includes an elastomeric membrane enclosed or partially enclosed about a main chamber. The implant is adapted to expand when filled with a fluid. The membrane includes an outer zone formed from at least one outer elastomeric layer; an inner zone formed from at least one inner elastomeric layer; and a middle zone formed from at least one elastomeric middle layer positioned between a least a portion of the outer zone and at least a portion of the inner zone. The implant is configured such that the middle zone is under contraction from a contracting force provided by the outer zone or the inner zone. A method of forming a fluid-filled adjustable implant for volumetrically altering, replacing, expanding, or augmenting tissues is also provided herein.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/726,198 filed on Nov. 14, 2012, which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to fluid-filled inflatable chamberedprosthetic implants and methods of fabrication thereof, which areemployed to volumetrically alter, replace, expand, or augment tissues,and, more particularly, to adjustable implants formed from self-sealingelastomeric membranes.

2. Description of Related Art

Breast reconstruction after mastectomy presents challenges as a resultof tissue loss and scarring. The tight chest-wall skin can often requireskin grafting to replace lost tissue. Expanding the skin is a moredesirable method to avoid skin grafting. Temporary skin expanders can beutilized but require eventual removal and replacement with theappropriate permanent implant. The multiple surgical procedures aredifficult for the patient and introduce additional risks and costs. Thisinvention will make a single surgery possible with slow expansion of thetissues remaining after the mastectomy. The implant can potentially beadjusted at any time, even years after the initial surgery.

Many breast implants are commercially available. A single chamber designis most common, and is available in a variety of fixed volumes toproduce a range of sizes and shape characteristics from about 80 to 800cubic centimeters. As used herein, “chamber” refers to the interiorportion of a breast implant, which is enclosed by an outer shell ormembrane. As is known by those skilled in the art, the interior portionof an implant may also be referred to as a lumen. The implants aregenerally filled with silicone gel or saline. Viscoelastic siliconeshells of all implants are very similar in composition, but vary inthickness, texture, and surface treatments. There are very significantdifferences with respect to the filling materials. The silicone gelimplants generally have more natural properties, with fewer noticeableedges and rippling effects. The viscosity of the silicone gel reducesfluid motion that results in these beneficial properties. The siliconegel filling the implant may alter over time to become firmer, softer,and change in elasticity, depending on its composition. Historically, amajor complication has been gel bleed leading to capsular contractionand tissue toxicity to the patient. Many gel-filled implants haveadditional barrier coatings or layers to lessen the diffusion ofsilicone into the tissues. Diffusion can be reduced, but not eliminated.

Saline implants were developed to eliminate complications related tofluid bleed. Saline is biocompatible and able to be absorbed withouttissue toxicity complications in the event of a slow bleed or rupture ofthe implant. The low viscosity of saline allows for significant fluidmotion leading to deformation of the fluid-filled shell. The wave andripple motion is often visible through the overlying tissue. This is amore significant complication in cases where there are not significantamounts of tissue surrounding the implant. The deformation of theviscoelastic membrane can cause the surrounding tissue to scar andcontract, distorting and hardening the feel of the implant. Salineimplants are often placed deep under muscle tissue of the chest andslightly overfilled to prevent complications.

Shell coatings and texturing have been developed to reduce capsularcontraction, with reasonable success. The variable surface treatmentsall work by enabling tissues to adhere and distribute forces responsiblefor contracture. The materials utilized to form, coat, and fill theimplants have resulted in a wide variety of available designs. Size andshape alone produce many options. The designs become more involved whenmulti-chamber and variable volumetric designs are considered.Variability of volume during surgery allows for adjustments to be madefor general size and symmetry. Access ports and valves are used toinflate or deflate the implant. In some cases, the filling tube is leftin place for a short period to allow for further adjustmentspost-surgery. This adjustability is a desirable and, often, a necessaryfeature in the case of tissue expanders.

Multi-chamber implants predominantly consist of an inner chamber and anouter chamber filled with silicone, saline, or a combination of both.The combination of chambers allows for greater variability in size andshape characteristics. Currently available models have a doublemembrane, double chamber design, in which an outer chamber has a fixedvolume of gel and an adjustable inner chamber is filled with saline.These implants provide a very natural appearance and feel with the addedadvantage of temporary adjustability. These more complex designs havebeen found to be less resistant to shear forces in areas where there arejunctions between the membranes and valve port.

Implants are intended to safely provide a natural feel and appearance,while minimizing leakage and contracture. Therefore, there is a need foran implant that achieves necessary performance and safety. It would alsobe beneficial for the implant to remain adjustable following surgery, toallow for appropriate correction if the patient physically changes orhas different expectations after the surgery is completed. Suchadjustments must be performed in a safe manner, without increasing riskto the patient or requiring additional surgical procedures. The implantshould also be configured to adjust for minor leakages over time. Theimplants and methods of formation thereof provided herein address someor all of these needs.

SUMMARY OF THE INVENTION

The present invention is of particular use in relation to breastreconstruction and augmentation, but is not limited to this field. Forpurposes of illustration and description, breast implants will beutilized as exemplary of the invention. Variations of the invention canbe utilized for tissue volume replacement and as a tissue expandingdevice to form tissues in post-traumatic surgery or in advance ofplanned surgery to prepare tissue flaps. As such, the invention can beemployed as a permanent prosthesis or temporary device, as indicated.Methods of manufacture make custom forms of this invention possible atan accessible cost. As such, this invention can be employed in planned,highly invasive surgeries, such as large tumor removal. An implant canbe fabricated in advance to replace the desired volume and form oftissues removed. As such, the implant can be utilized to slowly beexpanded or contracted over time to achieve the desired shape allowingtissues to slowly conform in a safe and predictable manner.

In general, the invention provides for an implant consisting of acontinuous, preferably self-sealing, elastomeric membrane design thatcan be configured to produce a variety of implant options. By nature ofits design, the membrane produces a different feel than current implantmembranes. These properties may be utilized to the advantage of variousimplant designs. In one preferred and non-limiting embodiment, theself-sealing nature of the membrane allows for adjustability without theneed of special ports and filling valves. Some possible breast implantconfigurations will be described for purposes of summarizing thisinvention and making attributes of the membrane apparent as they relateto breast implant shells.

Therefore, in accordance with certain aspects of the invention and inone preferred and non-limiting embodiment, provided is an adjustableimplant for volumetrically altering, replacing, expanding, or augmentingtissues. The implant includes an elastomeric, preferably self-sealing,membrane enclosed or partially enclosed about a main chamber. Theimplant is adapted to expand when filled with a fluid. The membraneincludes an outer zone formed from at least one outer elastomeric layer;an inner zone formed from at least one inner elastomeric layer; and amiddle zone formed from at least one elastomeric middle layer positionedbetween a least a portion of the outer zone and at least a portion ofthe inner zone. The implant is configured such that the middle zone isunder contraction from a contracting force provided by the outer zone orthe inner zone.

According to a further aspect of the invention and in another preferredand non-limiting embodiment, provided is a method of forming afluid-filled adjustable implant for volumetrically altering, replacing,expanding, or augmenting tissues. The method includes forming a firstzone of an elastomeric membrane defining at least one partially enclosedvoid space. The first zone includes at least one elastomeric layer. Themethod further includes: expanding a volume of the void space, therebyexpanding the first zone; forming a second zone including one or moreelastomeric middle layers on the first zone; reducing the volume of thevoid space, thereby contracting the first zone and the second zone; andforming a third zone including at least one elastomeric layer on thesecond zone. Thus, an elastomeric membrane including a first zone, asecond zone, and a third zone is formed. The method further includes thestep of forming an adjustable implant from the elastomeric membrane byenclosing the void space to form at least one chamber.

These and other features and characteristics of the present invention,as well as the methods of use and functions of the related elements ofstructures and the combination of parts and economies of manufacture,will become more apparent upon consideration of the followingdescription and the appended claims with reference to the accompanyingdrawings, all of which form a part of this specification, wherein likereference numerals designate corresponding parts in the various figures.It is to be expressly understood, however, that the drawings are for thepurpose of illustration and description only and are not intended as adefinition of the limits of the invention. As used in the specificationand the claims, the singular form of “a”, “an”, and “the” include pluralreferents unless the context clearly dictates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the advantages and features of the preferred embodiments of theinvention have been summarized herein above. These embodiments alongwith other potential embodiments of the device will become apparent tothose skilled in the art when referencing the following drawings inconjunction with the detailed descriptions as they relate, to thefigures.

FIG. 1 is a sagittal view of a female human body through the left breastshowing anatomical detail along with in situ placement of an adjustableimplant, according to the principles of the invention;

FIG. 2 is a cross-sectional view of a casting mandrel for forming anelastomeric membrane of an adjustable implant, according to theprinciples of the invention;

FIG. 3 is a cross-sectional view of a portion of an elastomeric membraneformed from the mandrel of FIG. 2, during a subsequent processing step,according to the principles of the invention;

FIG. 4 is a cross-sectional view of a portion of the elastomericmembrane of FIG. 3, during a subsequent processing step, according tothe principles of the invention;

FIG. 5 is an adjustable implant formed from the elastomeric membrane ofFIG. 4, according to the principles of the invention;

FIG. 6 is a cross-sectional view of a casting mandrel for forming anelastomeric membrane of an adjustable implant, according to theprinciples of the invention;

FIG. 7 is a cross-sectional view of a portion of an elastomeric membraneformed from the mandrel of FIG. 6, during a subsequent processing step,according to the principles of the invention;

FIG. 8 is a cross-sectional view of a portion of the elastomericmembrane of FIG. 7, during a subsequent processing step, according tothe principles of the invention;

FIG. 9 is an adjustable implant formed from the elastomeric membrane ofFIG. 8, according to the principles of the invention;

FIG. 10 is a cross-sectional view of a casting mandrel for forming anelastomeric membrane of an adjustable implant, according to theprinciples of the invention;

FIG. 11 is a cross-sectional view of a portion of an elastomericmembrane formed from the mandrel of FIG. 10, during a subsequentprocessing step, according to the principles of the invention;

FIG. 12 is a cross-sectional view of a portion of the elastomericmembrane of FIG. 11, during a subsequent processing step, according tothe principles of the invention;

FIG. 13 is an adjustable implant formed from the elastomeric membrane ofFIG. 12, according to the principles of the invention;

FIG. 14 is a cross-sectional view of an elastomeric membrane for anadjustable implant, according to the principles of the invention;

FIG. 15 is a cross-sectional view of the elastomeric membrane of FIG. 14in an inverted position, according to the principles of the invention;

FIG. 16 is a cross-sectional view of an adjustable implant formed fromthe elastomeric membrane of FIG. 14, according to the principles of theinvention;

FIG. 17 is a cross-sectional view of a casting mold for forming anelastomeric membrane, according to the principles of the invention;

FIG. 18 is a cross-sectional view of a portion of an elastomericmembrane formed from the mold of FIG. 17, according to the principles ofthe invention;

FIG. 19 is a cross-sectional view of an apparatus for secondary castingfor forming additional elastomeric layers on the portion of theelastomeric membrane of FIG. 18, according to the principles of theinvention;

FIG. 20 is a cross-sectional view of a processing step for forming anelastomeric membrane from the portion of the membrane of FIG. 18contained within the apparatus of FIG. 19, according to the principlesof the invention;

FIG. 21 is a cross-sectional view of a processing step for forming anelastomeric membrane from the portion of the membrane of FIG. 18contained within the apparatus of FIG. 19, according to the principlesof the invention; and

FIG. 22 is a cross-sectional view of an adjustable implant formed fromthe elastomeric membrane of FIG. 21, according to the principles of theinvention.

DESCRIPTION OF THE INVENTION

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “lateral”,“longitudinal”, and derivatives thereof shall relate to the invention asit is oriented in the drawing figures. However, it is to be understoodthat the invention may assume alternative variations and step sequences,except where expressly specified to the contrary. It is also to beunderstood that the specific devices and processes illustrated in theattached drawings, and described in the following specification, aresimply exemplary embodiments of the invention. Hence, specificdimensions and other physical characteristics related to the embodimentsdisclosed herein are not to be considered as limiting.

With reference to FIG. 1, a sectional view of an implant 12 placedwithin the left female human breast is illustrated. The implant 12,according to a preferred and non-limiting embodiment of the invention,is in a sub-muscular anatomical position under the pectoralis chestmuscle 5. Alternatively, the implant can be positioned sub-muscularly orin sub-glandular placement. There are variations on these placements,but these two categories of placement are the most common practice. Thesectional view of FIG. 1 provides basic anatomical landmarks forclarity. The implant 12 is posteriorly positioned against the chest walltissues and underlying ribs 6. Anteriorly, the implant 12 may bepositioned under the chest muscle tissue 5 with the greatest muscularcoverage enveloping the superior anterior aspects of the implant 12.Anterior to the muscle tissues 5 are the intact subcutaneous fat 4 andmammary glands 2. The nipple 3 is the most anterior structure to theimplant 12.

The implant 12 consists of multiple layers of an elastomeric membrane,also referred to as a shell. Generally, there are severalhigh-performance silicone elastomer layers for enhanced shell integrity.Variable elastomers are utilized to provide a membrane with self-sealingproperties. Although the membrane may include numerous layers, thelayers may be generally classified in three zones or regions, namely, aninner zone 18, a middle zone 19, and an outer zone 20.

The inner zone 18 has one or more elastomeric layers that are strong andhighly resistant to permeability. The layers of the inner zone 18 remainelastomeric and have significant ability to stretch and return to theiroriginal shape. These inner zone 18 layers are cured and set to adesired volume and shape, which encapsulates at least one chamber, suchas outer chamber 26, of the implant 12.

The middle zone 19 consists of multiple layers of softer elastomericmaterial to envelop the inner zone 18 layers in a significantly expandedstate. The middle zone 19 may be thicker than the inner zone 18 or theouter zone 20. During formation of the membrane, the inner zone 18 isexpanded to allow for the larger volumetric form to be established. Oncethe middle zone 19 is cured, the inner zone 18 and the middle zone 19are retracted to a volume and shape representative of the inner zone 18in its original cured shape. Thus, the softer middle zone 19 is insignificant contraction as it is forced to conform to a lesser volume.The outer zone 20 layers are then formed to envelope the middle zone 19layers. The outer zone 20 has similar or identical properties to theinner zone 18 layers, being elastomeric, yet strong and resistant.

The resultant membrane consists of a middle zone 19 that is thicker andformed from softer elastomeric membrane, under contraction. The middlezone 19 is sandwiched between the inner zone 18 and the outer zone 20 ofstronger and more stable elastomeric compounds. The resultant membranehas a total thickness of about 0.75 mm to 2.25 mm, and more preferablybetween about 1.0 mm and 1.25 mm. However, for certain applications, themembranes may have a total thickness below 0.75 millimeters or totalthickness in excess of 2.25 millimeters. Furthermore, the membrane maybe different thicknesses at different areas of the implant 12.

The three-zone configuration facilitates the self-sealing capability ofthe membrane. However, the design and configuration of the membrane isnot limited to the three-zone configuration. Other arrangements ofelastomeric layers may also be employed to provide the self-sealingability of the membrane. Furthermore, as will be appreciated by onehaving ordinary skill in the art, manipulation of these zone layers andtheir configuration will produce further advantages of this invention.For example, multiple layers under contraction will increase theintegrity and self-sealing potential of the membrane. Thickness of thelayers under contraction also relates directly to integrity of themembrane. Therefore, a balance between the optimal number of layers andlayer thickness should be established for particular applications.

The three-zone membrane can be punctured with a non-coring needle toaccess one or more chambers enclosed by the membrane. Non-coring needlesare used to puncture the membrane without removing any of the siliconematerial forming the membrane layers. The geometry of a non-coringneedle spreads and expands the silicon at the entry site. Uponretraction of the needle from the membrane, the silicone self-seals atthe penetration site. The silicone must be under contractive forces toself-seal. This contraction is achieved by retaining the siliconemembrane under mechanical compression from other elastomeric layers.

The self-sealing properties of the membrane produces an implant shellexhibiting properties different from existing implants. The compressionof the middle zone 19 changes how the inflation forces are manifested interms of the general feel of the implant 12. More specifically, theimplant 12 can be varied in design to produce a more natural feel withless of an inflated or balloon characteristic. Furthermore, theproperties of the membrane introduce a favorable variable that can beincorporated in various single or multiple chamber designs. For example,it is possible to alter the characteristics of the membrane to produce asaline-filled implant with more silicon-like characteristics.

It may be preferred to fill the chamber with biocompatible fillers, suchas saline or saline with biocompatible thickening agents, so that in theevent of leaking, the saline is naturally absorbed. Thickening agentscan be designed to provide additional sealing ability from within theimplant. Methycellulose has a high molecular mass and can be added tothe saline to give it gel-like properties. Aqueouscarboxy-methylcellulose has proven biocompatibility and is utilized insome cosmetic filling agents. Polyethylene glycol (PEG) and saline wouldalso be a suitable combination with thickening characteristics. The highmolecular mass of PEG and other similar thickening agents will reducethe risk of leakage from the membrane. Furthermore, membranes of breastimplants are generally made as thin as possible to achieve a softerfeel. Thinner membranes impose greater risks with respect to puncture,capsular contraction, and gel or fluid bleeds. The three-zone shellinherently allows for slightly thicker and safer designs.

Having generally discussed the structure of the elastomeric membrane andfluid-filled adjustable implant, methods of manufacture of membranes andimplants will now be described in detail. Additionally, furtherembodiments of an implant formed from an elastomeric membrane are alsodiscussed. As will be appreciated by one of ordinary skill in the art,the manufacturing possibilities of this invention are extensive withrespect to methods and materials. Drip casting around a mandrel is thetraditional method of forming the primary shell of a breast implant. Thereverse process of drip casting into a mold cavity can be an effectivealternate approach. To illustrate the alternate manufacturing steps,preferred manufacturing processes using both casting methods arediscussed herein. FIG. 2 through FIG. 16 are all based on formingviscoelastic membranes around mandrels. FIG. 17 through FIG. 22illustrate forming viscoelastic membranes by means of molding.

With reference to FIGS. 2-16, methods of forming an elastomeric membraneby drip casting about a mandrel 17 are discussed herein. Generally, theinner zone 18 layers are formed on the mandrel 17. The mandrel 17 isthen wasted, collapsed, or removed from the formed layers. There aremany potential materials that can be utilized to form the mandrel 17.Gypsum plaster is a good example; however, various plastics could beemployed as well. A plastic mandrel can be mechanically collapsed,softened with solvents, or heated to aid in removal without damaging thesilicone castings. Gelatinous substances are another option that canprovide sufficient stability to expand a membrane and form a mandrelthat can be wasted and removed. Agar or agar-agar is one such form of apolysaccharide that can be molded into firm stable shapes. Thepossibilities for casting are extensive and different techniques may beemployed for various applications of this invention.

An expansion medium 22 is utilized to expand the formed layers duringlater steps of the casting process. Such a medium 22 is necessary toretain a previously cast membrane in a desired expanded state, as wellas to support a membrane volume in a retracted state. The expansionmedium 22 has many possible choices of materials and techniques ofemployment. Gasses and fluids under pressure are the simplest mediumsthat can be used. Agar and other materials that can be poured and castto a fixed volume and shape can also be utilized. Agar has a low meltingpoint, which allows it to be liquefied for removal or recast asrequired. Beads are another option that can produce fixed volumes ofvariable shapes. The advantages and disadvantages of various expansionmediums will be apparent based on the requirements of the particularstage of manufacture.

With reference to FIGS. 2-6, a method of forming a preferred andnon-limiting embodiment of an implant 10 by drip casting about a mandrel17 is provided. FIG. 2 is a sectional view of the drip casting mandrel17. The mandrel 17 is formed from a material that will be destroyedafter the inner zone 18 layers are cast. Thus, the mandrel 17 can bedescribed as a waste drip casting mandrel. The mandrel 17 can be cast ingypsum plaster. The gypsum plaster is a viable option, as it can be castvery thin and can be easily removed by mechanical means and/or dissolvedwith sodium bicarbonate and water. Multiple elastomeric layers are dripcast onto the mandrel 17 to form the inner zone 18 of the membrane. Theinner zone 18 visco elastic layers must be very durable, essentiallyimpermeable, exhibit stable memory characteristics, and still remainvery elastic.

In FIG. 3, the mandrel 17 has been wasted and the inner zone 18 shellhas been filled with expansion medium 22 through a filling tube 21 forthe purpose of expanding the shell to a desired volume. The expansionmedium 22 is required to be a stable medium that can be altered involume. The filling tube 21 has three functions. It inflates the innershell 18, allowing the expansion medium 22 to pass through it and fillthe expanded volume. Once the desired form is achieved, the filling tube21 becomes a supporting handle, which creates a drip casting mandrel toapply the middle zone 19 viscoelastic layers. The middle zone 19 layersare applied directly on top of the inner zone 18. The middle zone 19layers have a tacky, but cured state, which remains soft and elastic.Such pliable characteristics allow these layers to be put in a state ofcompression.

FIG. 4 illustrates the third drip casting state. In this form, a portionof the expansion medium 22 has been removed to return the membrane to avolume and shape representative of the original mandrel 17. The fillingtube 21 is utilized to create a vacuum retracting the inner zone layersand compressing the middle zone layers 19 to conform thereto. The outerzone 20 layers are drip cast to encase the middle 19 and inner zone 18layers. The three-zone shell is complete when the outer zone 20 layersare cured. These outer zone 20 viscoelastic layers must be very durable,essentially impermeable, exhibit stable memory characteristics, andstill remain very elastic. The layers of the outer zone 20 areessentially the same as, or similar to, the inner zone 18 viscoelasticlayers.

FIG. 5 illustrates a non-limiting and preferred embodiment of theimplant 10 formed from a three-zone membrane in its completed state. Toproduce the implant 10, the expansion medium 22 is removed producing avoid shell. The shell is cleaned and surplus membrane, formed along thefilling tube 21, is trimmed away. The flange remaining around the holethat remains in the middle of the posterior aspect of the implant isinverted inward and a plug 23 is vulcanized to seal the implant 10. Theplug 23 is formed from a viscoelastic material, similar to the materialthat forms the middle zone 19. The plug 23 functions as a self-sealinginjection port that can be utilized to pre-fill a main chamber 25 of theimplant 10 enclosed by the membrane to a desired volume prior toimplantation. This plug 23 may take a variety of forms andconfigurations, such as a one-way valve, a flapper valve, an elasticvalve, and the like. Further, the plug 23 may include one or moreapertures or conduits through which to insert specified fluids intovarious areas of the implant 12. Biocompatible thickening agents canalso be pre-filled prior to sealing the implant 10. The implant 10 isfilled or partially filled with a fluid, such as saline, prior toimplantation to a patient.

With reference to FIGS. 6-9, a method of manufacture is illustrated forthe implant 12 depicted in FIG. 1. FIG. 6 is sectional view of adual-chamber drip casting mandrel 17 used to form the inner zone 18 ofthe implant 12. The mandrel 17 is formed to a desired shape out of amaterial that will be destroyed after the inner zone 18 layers are castto its form. The mandrel 17 can be described as a waste drip castingmandrel. The mandrel 17 can be cast in gypsum plaster. The gypsumplaster can be cast very thin and can be easily removed by mechanicalmeans and/or dissolved with sodium bicarbonate and water. Multipleelastomeric layers are formed on the mandrel 17 to form the inner zone18. The inner zone 18 viscoelastic layers must be very durable,essentially impermeable, exhibit stable memory characteristics, andstill remain very elastic.

In FIG. 7, the dual chamber mandrel 17 has been wasted and both chambersof the inner zone 18 shell have been filled with the expansion medium 22for the purpose of expanding the shell and retaining it to a desiredvolume. The filling tube 21 has three functions. It inflates the innershell allowing the expansion medium 22 to fill the expanded volume. Oncethe desired form is achieved, the filling tube 21 becomes a supportinghandle creating a drip casting mandrel to apply the middle zone 19viscoelastic layers. The middle zone 19 layers are formed directly onthe inner zone 18 and cured. The middle zone 19 layers are required toattain a tacky, but cured state, which remains soft and elastic. As inthe previously described embodiment, the pliable layers are capable ofbeing put in a compression state.

FIG. 8 illustrates the third drip casting state. In this form, a portionof the expansion medium 22 is removed to return the membrane to a volumeand shape representative of the original mandrel 17. The filling tube 21is utilized to create a vacuum retracting the inner zone 18 layers andcompressing the middle zone 19 layers to conform thereto. The outer zonelayers 20 are drip cast to encase the middle 19 and inner zone 18layers. The three-zone membrane is completed when the outer zone 20layers are cured. These outer zone 20 viscoelastic layers must be verydurable, essentially impermeable, exhibit stable memory characteristicsand still remain very elastic. Thus, they are essentially the same as orsimilar to the inner zone 18 viscoelastic layers.

FIG. 9 illustrates a preferred and non-limiting embodiment of theimplant 12 in a completed state, formed from the elastomeric membranedepicted in FIGS. 7 and 8. To form the implant 12, the expansion medium22 is removed producing a void shell. The shell is cleaned byappropriate measures. After cleaning, a smaller inner chamber 27 of themembrane is folded into an outer chamber 26 forming an implant in whichthe outer chamber 26 encloses the inner chamber 27. Thus, the innerchamber 27 membrane is inverted in its final position. A portion of thecontinuous membrane formed along the filling tube 21 becomes thetermination of the membrane. As this portion of the membrane exits theposterior aspect the implant 12, surplus is trimmed away. Next, a plug23 is vulcanized to seal the implant 12. The plug 23 is formed fromviscoelastic material similar to the middle zone 19. The plug 23functions as a self-sealing injection port that can be utilized topre-fill the outer chamber 26 and inner chamber 27 of the implant to adesired volume prior to implantation. Biocompatible thickening agentscan also be pre-filled prior to sealing the implant. In this finalconfiguration, the implant 12 has a continuous viscoelastic membraneforming two self-sealing independent chambers. The implant 12 is filledor partially filled with a fluid, such as saline, prior to implantationto a patient.

With reference to FIGS. 10-13, a method of manufacture of a furtherembodiment of an adjustable implant 13 is illustrated. Morespecifically, FIG. 10 is sectional view of a three-chamber drip castingmandrel 17 used for the initial forming of implant 13, according to apreferred and non-limiting embodiment of the invention. The mandrel 17is formed to a desired shape out of a material that will be destroyedafter the inner zone 18 layers are cast to its form. The mandrel 17 canbe described as a waste drip casting mandrel 17. The mandrel 17 can becast in gypsum plaster. The gypsum plaster can be cast very thin and canbe easily removed by mechanical means and/or dissolved with sodiumbicarbonate and water. Multiple elastomeric layers are drip cast to themandrel 17 to form the inner zone 18. The inner zone 18 viscoelasticlayers must be very durable, essentially impermeable, exhibit stablememory characteristics, and still remain very elastic.

In FIG. 11, the three-chamber mandrel 17 is wasted and the main chamberof the inner zone 18 shell is filled with the expansion medium 22 forthe purpose of expanding the shell and retaining it to a desired volume.The filling tube 21 requires a retaining clip 24 to seal the neck to theouter chamber 26 and also pull the two smaller chambers (collectivelyinner chamber 27) away from the outer chamber 26. The filling tube 21has three functions. It inflates the inner zone 18 shell of the outerchamber 26 allowing the expansion medium 22 to pass through it and fillthe expanded volume. Once the desired form is achieved, the filling tube21 becomes a supporting handle creating a drip casting mandrel. Themiddle zone 19 viscoelastic layers are applied directly to portions ofthe inner zone 18. In a preferred and non-limiting embodiment, themiddle zone 19 viscoelastic layer is only drip cast on the outer chamber26. The middle zone 19 layers are required to attain a tacky, but curedstate which remains soft and elastic. These pliable characteristics meanthat the middle zone 19 layers can be placed in a state of compression.

FIG. 12 illustrates the third drip casting state. In this form, aportion of the expansion medium 22 is removed to return the outerchamber 26 to a volume and shape representative of the original mandrel17. The expansion medium 22 is also added to the inner chambers 27 tofill them to a volume and shape representative of the original mandrel17. The filling tube 21 is utilized to create a vacuum pressure, therebyretracting the entire structure and compressing the middle zone 19layers to conform thereto. The outer zone 20 layers are drip cast toencase the middle zone 19 and inner zone 18 layers. The three-chambershell is complete when the outer zone 20 layers are cured. These outerzone 20 viscoelastic layers must be very durable, essentiallyimpermeable, exhibit stable memory characteristics, and still remainvery elastic. They are essentially the same as or similar to the innerzone 18 viscoelastic layers. The final three-chamber shell consists ofan outer chamber 26 shell which has the three layer self-sealingproperties. The two smaller chambers (collectively inner chambers 27)only include inner zone 18 and outer zone 20 layers.

FIG. 13 illustrates a preferred embodiment of the implant 13, formedfrom the membrane layers of FIGS. 11 and 12, in its completed state. Theexpansion medium 22 is removed, producing a void shell. The shell iscleaned through appropriate measures. The two smaller chambers(collectively inner chambers 27) are folded into the outer chamber 26.Thus, the inner chamber 27 membrane has an inverted outer aspect andnon-inverted inner aspect in its final position. A portion of thecontinuous membrane along the filling tube 21 forms the ends of themembrane. A port for accessing the outer chamber 26 of the membrane ispositioned at the ends of the membrane. Surplus material is trimmed fromthis portion of the membrane. A plug 23 is vulcanized to seal theimplant 13 in the port. The plug 23 is to be formed from viscoelasticmaterial similar to the middle zone 19. The plug 23 functions as aself-sealing injection port that can be utilized to pre-fill the outerchamber 26 and inner chamber 27 of the implant 13 to a desired volumeprior to implantation. Biocompatible thickening agents can also bepre-filled prior to sealing the implant. It is noted that the innerchamber 27 may be perforated to allow fluid communication of allchambers. This configuration utilizes the inner structures to providebaffling characteristics to calm fluid motion of the liquid utilized tofill the chambers. The implant 13 is filled or partially filled with afluid, such as saline, prior to implantation to a patient.

With reference to FIGS. 14-16, a method of forming a further preferredand non-limiting embodiment of an adjustable implant 14 is illustrated.FIG. 14 depicts a completed shell formed by drip casting around amandrel, including inner zone layers 18, middle layers 19, and outerzone layers 20. The completed shell is similar in shape to completedshells illustrated in FIG. 6 and FIG. 7. In FIG. 14, the expansionmedium 22 was removed producing a void shell. The shell was also cleanedafter the expansion medium 22 was removed. The shell is inflated enoughto maintain its shape and a temporary plug 30 is positioned near anopening of the shell. Viscoelastic tendrils 29 are formed or vulcanizedon one of the chambers of the shell.

FIG. 15 depicts the next formation stage, where the entire membrane isinverted upon itself, such that tendrils 29 extend inward into the innerchamber 27. The final configuration of the implant 14 with tendrils 29is illustrated in FIG. 16. The smaller inner chamber 27 with tendrils 29is folded into the outer chamber 26. The inner chamber 27 is notinverted in its final position. The tendrils 29 expand into the outerchamber 26 providing stability to the final form and bafflingcharacteristics to calm fluid motion in the outer chamber 26. The outerchamber 26 membrane remains inverted in its final position. A portion ofthe continuous membrane formed along the filling tube 21 forms thetermination of the membrane. As this portion of the membrane exits theposterior aspect of the implant 13, the surplus membrane material istrimmed. A plug 23 is vulcanized to seal the implant 14. The plug 23 isto be formed from viscoelastic material similar to the middle zone 19.The plug 23 functions as a self-sealing injection port that can beutilized to pre-fill the outer chamber 26 and inner chamber 27 of theimplant 14 to a desired volume prior to implantation. Biocompatiblethickening agents can also be pre-filled prior to sealing the implant.This final configuration of the implant 14 has a continuous viscoelasticmembrane forming two self-sealing independent chambers, namely outerchamber 26 and inner chamber 27. The implant 14 is filled or partiallyfilled with a fluid, such as saline, prior to implantation to a patient.

With reference to FIGS. 17-22, a method of manufacturing an implant 11is depicted. Unlike previously described embodiments of the invention,the implant 11 is manufactured by drip casting into a mold cavity. Theprocess is essentially the reverse from previous examples and uses amolding method to form the various layers in molding cavities instead ofexternally around drip casting mandrels. The layers are cast and curedin the reverse order, starting with the layers of the outer zone 20.FIG. 17 illustrates a mold utilized to produce the viscoelastic layersof the outer zone 20, which are very durable, essentially impermeable,exhibit stable memory characteristics, and still remain very elastic. Inthis casting process, the mold 17 b is reusable and may be made fromglass or rigid plastic. A clear material is generally preferable,allowing for visual inspection during the casting process. Variousmethods of casting may be employed from simple manual techniques tomechanical spin casting. The purpose of this initial stage is to producea complete form of the viscoelastic layers of the outer zone 20 as seenin FIG. 18. This outer shell may alternately be produced by means ofdrip casting upon a mandrel. Regardless of the method, the viscoelasticlayers of the outer zone 20 are cured to the required shape and providethe base upon which the remaining layers are laminated. FIG. 18illustrates a void shell of the outer zone 20 layers.

FIG. 19 illustrates the apparatus required to cast the remaining layers.The outer body of the apparatus 33 is rigid with an evacuation valve 34and an internal bladder 17 c. The purpose of this apparatus is to createan internal mold cavity that can be expanded and retracted through thelaminating process. The bladder 17 c has a base shape reflective of thefinal form of the preferred and non-limiting embodiment of the implantillustrated in FIG. 5. The bladder 17 c has elastic properties andstrong memory of form. It will require perforations to allowcommunication between the mold cavity and evacuation chamber 35 createdby the outer body of the apparatus 33. In FIG. 19, the previously formedouter zone 20 viscoelastic layers are positioned within the bladder 17 cand retracted to conform to the matching shape of the mold cavitycreated by the bladder 17 c. A slight vacuum pressure is required tohold the outer zone 20 layers in place. The bladder 17 c and outer zone20 layers are sealed around a collar of the apparatus 33 body. Thevacuum pressure is maintained by utilizing the evacuating valve 34. Incertain embodiments, the contact surface between the bladder 17 c andthe viscoelastic layers of the outer zone 20 requires lubrication toequalize and marry the conforming shapes. Once positioned and retained,the apparatus 33 is configured to expand the bladder 17 c along with theouter zone 20 viscoelastic layers to a desired size and shape.

In FIG. 20, the complex of the bladder 17 c and the previously formedouter zone 20 layers are expanded and retained in an expanded form byclosing the evacuation valve 34 to seal the evacuation chamber 35. Theexpanded mold cavity is ready to laminate the middle zone 19 layers. Themiddle zone 19 layers are required to attain a tacky, but cured statewhich remains soft and elastic. These middle zone 19 layers may havepliable characteristics that allow the layers to be placed in a state ofcompression. The middle zone 19 layers are cast in one or more layers bymanual or mechanical means, similar to the previously cast outer zone 20layers. After casting of the middle zone 19 layers is complete, thelayers are subjected to compression by opening the evacuation valve 34.This allows the bladder 17 c to return to its original memory shape withthe laminated outer zone 20 layers and middle zone 19 layers. Theprocess of retraction may be done in a cured or partially cured state toallow manipulation of desired characteristics of the membrane complex.

In FIG. 21, the apparatus is configured in a final molding state. Theouter zone 20 and middle zone 19 laminated membranes are retracted to ashape representative of the final form of the embodiment of the implant10 depicted in FIG. 5. Adequate vacuum pressure remains in theevacuation chamber 35 to stabilize the form for molding. The inner zone18 viscoelastic layers are cast in one or more layers by manual ormechanical means, similar to the previously cast layers. These innerzone 18 layers must be very durable, essentially impermeable, exhibitstable memory characteristics, and still remain very elastic. Once theinner zone 18 layers are cured, the three-zone membrane is complete andready for removal. The vacuum is released and the laminated implantshell is pulled through the collar of the apparatus 33 neck.

FIG. 22 illustrates the implant 11 in a completed state. The implant 11is essentially identical to the implant 10 illustrated in FIG. 5. Toproduce the completed implant 11, the void is cleaned by appropriatemeasures and surplus membrane that formed along the apparatus 33 collaris trimmed. The flange remaining around the hole that remains in themiddle of the posterior aspect of the implant 11 is inverted inward anda plug 23 is vulcanized to seal the implant. The plug 23 is formed fromviscoelastic material similar to the middle zone 19. The plug 23functions as a self-sealing injection port that can be utilized topre-fill the main chamber 25 of the implant to a desired volume prior toimplantation. Biocompatible thickening agents can also be pre-filledprior to sealing the implant. The implant 11 is filled or partiallyfilled with a fluid, such as saline, prior to implantation to thepatient.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements. For example, it is to beunderstood that the present invention contemplates that, to the extentpossible, one or more features of any embodiment can be combined withone or more features of any other embodiment.

The invention claimed is:
 1. An adjustable implant for volumetrically altering, replacing, expanding, or augmenting tissues comprising an elastomeric membrane enclosed or partially enclosed about a main chamber, which is adapted to expand when filled with a fluid, wherein the membrane comprises: an outer zone formed from at least one outer elastomeric layer; an inner zone formed from at least one inner elastomeric layer; and a middle zone formed from at least one elastomeric middle layer positioned between at least a portion of the outer zone and at least a portion of the inner zone, and wherein a volume enclosed by the middle zone at the time of curing is larger than each of a volume enclosed by the inner zone at the time of curing and a volume enclosed by the outer zone at the time of curing, resulting in compression of the middle zone by at least one of the outer zone and the inner zone wherein the membrane includes a first end and a second end positioned to form an opening for accessing an interior of the main chamber, and wherein a plug is provided in the opening.
 2. The adjustable implant of claim 1, wherein the middle zone is cured to a state that is softer than the inner zone or the outer zone.
 3. The adjustable implant of claim 1, wherein at least a portion of the middle zone is in a non-flowable, tacky state.
 4. The adjustable implant of claim 1, wherein at least a portion of the inner zone or the outer zone is resistant to permeability.
 5. The adjustable implant of claim 1, wherein the membrane is folded to form at least one inner chamber enclosed within at least a portion of the main chamber.
 6. The adjustable implant of claim 5, wherein the membrane is a single continuous membrane that forms the main chamber and the inner chamber.
 7. The adjustable implant of claim 6, wherein the at least one inner chamber is an annular chamber attached to an inner wall of the main chamber by a portion of the membrane.
 8. The adjustable implant of claim 7, wherein the annular chamber has a substantially “C”-shaped radial cross-section.
 9. The adjustable implant of claim 5, wherein a plurality of tendrils extend from at least a portion of the membrane enclosing the inner chamber.
 10. The adjustable implant of claim 9, wherein the tendrils extend from the outer zone of the membrane.
 11. An adjustable implant for volumetrically altering, replacing, expanding, or augmenting tissues comprising an elastomeric membrane enclosed or partially enclosed about a main chamber, which is adapted to expand when filled with a fluid, wherein the membrane comprises: an outer zone formed from at least one outer elastomeric layer; an inner zone formed from at least one inner elastomeric layer; and a middle zone formed from at least one elastomeric middle layer positioned between at least a portion of the outer zone and at least a portion of the inner zone, wherein the middle zone is under contraction from a contracting force provided by the outer zone or the inner zone, wherein the membrane is folded to form at least one inner chamber enclosed within at least a portion of the main chamber, and wherein at least a portion of the membrane enclosing the inner chamber is perforated.
 12. The adjustable implant of claim 1, wherein a thickening, agent is provided in an interior of the main chamber.
 13. The adjustable implant of claim 1, wherein the outer zone, middle zone, and inner zone have a total thickness of between about 0.75 mm and about 2.25 mm.
 14. The adjustable implant of claim 1, wherein the main chamber is filled or partially filled with a biocompatible fluid.
 15. The adjustable implant of claim 1, wherein a volume enclosed by the middle zone of the membrane is less than the volume enclosed by the middle zone at the time of curing. 